Research Journal of Applied Sciences, Engineering and Technology 1(3): 149-153, 2009
ISSN: 2040-7467
© M axwell Scientific Organization, 2009
Submitted Date: August 06, 2009
Accepted Date: August 17, 2009
Published Date: October 20, 2009
Shelf-life of Roasted Cashew Nuts as Affected by Relative Humidity, Thickness of
Polythene Packaging Material and Duration of Storage
S.V. Irtwange and A.O. Oshodi
Department of Agricultural and Environmental Engineering, University of Agriculture, Makurdi
Abstract: The effect of relative humidity, thickness of polythene packaging material and duration of storage
on the shelf life of roasted cashew w as determined to provide inform ation for pack aged roasted cashew nuts
marketers. For this study, split plot in Randomized Complete Block Design was used with a total number of
180 observations (3 relative humidity x 4 polythene thicknesses x 5 duration levels of storage x 3 replications)
each for moisture con tent, microbial coun t and quality index , which w ere measured using standard procedures.
The initial mean m oisture content, total fungal counts and percentage quality index of the nuts w ere fou nd to
be 1.17%db, 30CFU/g and 100% respectively, which were all deemed appropriate in comparison with the set
acceptable storage mo isture co ntent of 5.8%db, tolerable fungal levels of 10 3 and 10 4 /g and acceptable
percentage quality index of 45% for roasted cashew nuts which did not exceed its shelf-life and still deemed
fit for human consumption. The results of the study indicates that relative humidity, polythene thickness and
duration of storage have a highly significant effect (P#0.01) on m oisture content and quality index while for
the microbial count, polythene thickness and duration of storage has significant effect (P#0.05) with relative
hum idity show ing no n-sign ificance. For all levels of relative humidity an d polythen e thickness, m oisture
content and microbial count increased with increase in duration of sto rage w hile quality index decreased with
increase in duration of storage. As the polythene thickness increased at con stant storage duration, the moisture
content decreased. The moisture content of all the samples increased with increase in duration of storage at
constant polythene thickness level. As the thickness of the polythene packaging material increased, the amount
of moisture absorbed over time (in days) decreases; the total fugal grow th decreases, and the percentage qu ality
index increases. It is recommended that for the packaged roasted cashew nuts industry for poverty alleviation,
the most favourable polythene thickness of 0.95mm should be used. The best storage relative humidity was
determined in the study to be 47.2% under which conditions, storage period should not exceed 14 days for best
quality and value for money.
Key w ords: Polythene thickness, packaging material, roasted cashew nuts and shelf-life
INTRODUCTION
W orldwide, cashew nuts are an esteem ed an d high ly
priced food delicacy because of their pleasant taste and
flavour. The post-harvest processing, packaging and
marketing have been com mercialized an d mod ern
technology and regulations adopted in major producing
countries like India and Tanzania. In Nigeria ho wev er,
despite the cultivation of cashew in plantations and the
establishment of cashew-processing factories (Esuruoso,
1974), peasant pro cessin g and pack aging methods are still
com mon ly adop ted. Th e latter predisposes the nuts to
mou ld contamination especially during hawking of the
product, which usually are packaged in hand-knotted thin
polyethylene bags. There are no labels to indicate vital
information such as the name and address of producer,
nutritional contents, recommendations for storage and the
best-before-date for human consumption. H owe ver,
mycotoxicoses are becom ing increasingly implicated in
human and anima l pathology (Bacha et al., 1988). The
situation is worsened by consume rs’ reluctance to discard
fairly mouldy food samples such as cashew nuts. Cashew
seeds have no dormancy. They remain viable for one year
if dried to 9% moisture content and stored properly. The
kernels rank third after almonds and hazelnuts in the
international trade of tree nuts. The kernels constitute a
valua ble expo rt produ ct for confectionery and dessert
purpose s (Jaffe and M orton, 1995 ).
Shelf life is that length of time that food, drink,
medicine and other perishable items are given before they
are considered unsuitable for sale or consump tion. Shelf
life is different from expiration date; the form er relates to
food quality, while the latter refers to food safety. A food
that has passed its shelf life is still safe, but optimal
quality is no longer guaranteed. Shelf life is most
influenced by several factors: exposure to light and h eat,
transmission of gases including humidity, mechanical
stresses, and contamination by such things as microorganisms. Product quality is often mathematically
modelled around a single parameter (concentration of a
chem ical; comp ound, a m icrobiological index, or a
physical param eter), though this approach can miss
relevancy. Preservatives and antioxidants may be
incorporated into some food and drug products to extend
Corresponding Author: S. V. Irtwange, Department of Agricultural and Environmental Engineering, University of Agriculture,
Makurdi, Tell: +234-803-5885567
149
Res. J. Appl. Sci. Eng. Technol., 1(3): 149-153, 2009
their shelf life. Some companies use induction sealing
and vacuum pouches to assist in the extension of the shelf
life of their products. The principal factors that affect
shelf life are the nature of the food and the mechanisms
by which it undergoes deterioration; the size of package
in relation to volume; the atmosph eric condition which the
package is required to withstand during transit and before
use and the overa ll resistance of the package of moisture,
atmosphe ric gases and odours, including the closures and
folded areas (Dwe m, 1997). The shelf life of processed
food is determ ined by the type of food, the degree of
microbial destruction or inactivation achieved by the
process, control of hygiene during processing and
packaging, the barrier properties of the packaging
materials and the temperature during distribution and
packag e (Ade bajo and Diyaolu, 2003).
Roasted cashew nut can be consumed either directly,
or used as a raw material. In whichever form, the excess
has to be preserved for future us e. The greater value of
this product is lost to spoilage after a period of time due
to improper handling an d storage conditions and this
result in great loss of product and investment. Roasted
cashew nut is vulnerable to deterioration over time and
this result from improper packaging to adverse storage
conditions. The rate of this spoilag e is dependent on
moisture content of stored nuts; relative humidity of
storage enviro nme nt; perm eability of packaging m aterial;
ambient temperature and insect infestation. Based on
these effects, roasted cashew nuts deteriorate by m ould
growth, rancidity and insec t attack (Ayiko ye, 2004 ).
Since the society and most importantly investors
suffer great losses as a result of the deterioration of
polythene-packaged cashew nuts, it becomes imperative
to study and analyze the effect of the thickness of the
polythene used as the packaging material on the spoilage
rate under enviro nme ntal condition with a view to making
recom men dations base d on the resu lt of the ex perim ent.
material. Each of the samples were suspended in the
airspace containers co ntaining solution of dilute
tetraoxosulphate VI acid (sulphuric acid) of different
levels of dilution thus creating three relative hu midity
environm ents of 47.2% , 70.4% and 8 8.8% in accordance
with W east and Astle (1989). After insertion of the
samples and the solutions, the containers were closed and
exposed to ambient temperature. The set up was
monitored daily for four weeks (28 days). On the first
day, i.e. day zero (0), the moisture content, microbial
count and o rganoleptic tests were carried out. These tests
were repeated on day 7, day 14, day 21, and day 28. Three
replications were performed for each set up for the
samples.
Moisture content: The Gallen K amp vacu um o ven-air
method was used for moisture content test. About 10g of
sample was crushed in a mortar and about 5g bits was
measured into a crucible whose weight had been zeroed.
The crucible with the samples was then put into the oven
and dried at 103ºC for 4.5 hours. The weight of the
sample was taken again after they were cooled in the
desiccators. The percentage moisture content on dry ba sis
was calculated using % moisture content (dry basis) =
(chan ge in w eight/w eight of dry m atter) x 100.
Microbial count: The pour plate techniqu e was use d to
obtain the microbial count. Nine (9) ml of distilled water
was measured using a pipette into each of the sterile testtubes and w ere sterilized in an autoclave at 121ºC for 15
minutes after which they were brought out and coo led to
about body temperature. The roasted cashew nuts were
cut into small pieces with a sterile scalpel and 1g was
mixed with 9 ml of distilled water and then properly
shaken. The serial dilution was carried out to 10 G4 dilution
i.e. 1ml of the solution was drawn out using a pipette and
was introduced into a second test-tube containing 9ml of
distilled water and this was done serially until the last
tube was reached. A fresh pipette was used at each stage.
The potato dextrose agar was melted and cooled . Sterile
petri dishes were set out for each dilution and they w ere
labelled with the dilution number. 1ml of each dilution
was pipetted into the centre of the appropriate dishes,
using a fresh pipette for each dilution. Potato dextrose
agar was pou red into each of the plates, enough to cover
the 1ml solution in them. The medium was allowed to
solidify, then inverted and incubated at 37ºC for 24 hours.
The numbers of colonies were counted with the use of a
colon y cou nter.
MATERIALS AND METHODS
M aterials: The roasted cashew nuts used for this study
were procured in Obollo-Afor in Enugu State, Nigeria.
Packaging films (polythene) of three different thicknesses:
0.91mm, 0.93mm and 0.95mm and m osqu ito net. Plastic
air-tight containers were used as storage containers.
Equipment and machines used include GallenKamp
vacuum oven, desiccators, autoclave, incubator, weighing
scale, sealing machine, test tubes, petri dishes, pipettes,
mortar and pestle, crucibles (moisture test cans).
Chemicals and reagen ts include diluted tetraoxosulphate
VI acid (sulphuric acid), distilled water, potato dextrose
agar.
The cashew nuts were roasted in open pans (FAO,
2000). Twenty five gramm es (25g) of roa sted sample
seeds were tied in polythene bags of three different
thicknesses (0.91mm, 0.93mm, and 0.95mm) and a
control set using mosquito net, all purchased from
Modern Market, M akurdi, Benue State as its packaging
Quality index: Three students of the University o
Agriculture, Makurdi were trained to chew and report on
the overall acceptability in terms of taste, crispiness and
visible mould incidence of the samples in percentages.
Each person’s decision was independent of the other. The
cashew nuts were tasted on days 0, 7, 14, 21, and 28. The
nuts were reported as being very goo d (80% and abo ve),
good (60-79% ), fairly good (45-59%), fairly bad (40-
150
Res. J. Appl. Sci. Eng. Technol., 1(3): 149-153, 2009
44% ), bad (30-39% ) and v ery ba d (belo w 30% ) to
indicate the degree of quality.
80.5%RH while comparisons between 47.2 and 80.5%RH
were all statistically different. In the case of the microbial
count, 81.25, 37.5 and 50% non significance was
observed between 47.2 and 70.4, 47.2 and 80.5, and 70.4
and 80.5%RH respectively whereas for quality index, 50,
0 and 6.25% non-significance was sim ilarly observed. In
general, the greater the non significance percentage
difference, the closer the similarities between the levels of
measured parameters being compared.
Experimental Design: The experimental design for the
study is split plot in Randomized Complete Block Design
(RCBD) made up of three levels of packaging films
(polythene) of three different thicknesses: 0.91mm,
0.93mm and 0.95mm and mosquito net; three levels of
relative hum idity environmen ts: 47.2% , 70.4% and 88.8%
and five levels of days of storage (0, 7, 14, 21 and 28
days). The an alysis of variance (ANO VA ) and Fishers
Least Significant D ifference (F-LSD ) were carried out
using Genstat statistical package.
Effect of Polythene Thickness: The results show that as
the polythene thickness increased at constant storage day,
the moisture content decreased (Table 1). For example, at
storage day 14, the moisture content decreased from 4.54
to 2.11%db for 47.2%RH, 5.63 to 2.78%db for 70.4% RH
and from 6 .84 to 3.39% db for 80.5% RH . Similarly
microbial coun t decreased from 1 100 to 120, 2700 to 200
and 12400 to 500 CFU/g for 47.2, 70.4 and 80.5% RH
respectively whereas quality index increased from 63 to
80.5, 60 to 76.25 and 50 to 71% at same % RH values.
The analysis of variance (Table 2) show s highly
significant (P#0.01) polythene thickness effect on
moisture content and quality index while microbial count
is considered significant (P#0.05). A 2-tailed F-LSD test
at 5% level of significance shows that in the case of
47.2% RH, the 10 mean moisture content comparisons
were found to be statistically different for control but 10,
20 and 30% non-significance for 0.91, 0.93 and 0.95mm
respectively. Again 10% non-significance was observed
for 0.91, 0.93 and 0.95mm at 70.4%RH and 0.91 and
0.95mm at 80.5% RH while all other com parisons w ere
statistically different. In the case of microbial count, all 10
comparisons at 47.2%RH were non-significant while 40,
60, 60 an d 100% non-significance was observed at
70.4%RH for control, 0.91, 0.93 and 0.95mm
respectively. Similarly, 10% non-significance for control
and 40% for 0.91, 0.93 and 0.95mm at 80.5%RH w as
observed. For quality index, 10 and 30% non-significance
was observed for control and 0.91mm while 20% was
observed for 0.93 and 0.95mm at 47.2% RH . The quality
index was also 10% non-significant for control and 20%
for 0.91, 0.93 and 0.95mm at 70.4%RH while 10, 20, 30
and 20% non-significance was recorded at 80.5%RH for
control, 0.91, 0.93 and 0.95mm respectively.
RESULTS AND DISCUSSION
Table 1 show s the results of the mean m oisture
content, total fungal counts and the percentage qu ality
index as affected by relative humidity, polythene
thickness and day s of storage. The various F-LSD s are
indicated for the purpose of mean comparisons while the
Analysis of Variance (ANOVA) is show n in Table 2. The
ANOVA table shows highly significant relative humidity,
polythene thickness an d days o f storage effect (P#0.01)
for moisture content and quality index while for the
microbial count, there was significant effect (P#0.05) for
polythene thickness an d days of stora ge w ith relative
hum idity showing non-significance. For all the shelf-life
param eters m easured, interaction was non -significa nt.
Effect of Relative Hum idity: For all the relative
hum idity and at all polythene thickness levels, moisture
content and m icrobial coun t increased w ith increase in
days of storage w hile quality inde x dec reased with
increase in days of stora ge (Table 1). For example, for
relative humidity of 47.2% and polythene thickness of
0.91mm, moisture content increased from 1.17 %db on
day 0 to 9.61 %db on day 28, microbial count increased
from 30 to 2100 CFU/g while quality index decreased
from 100 to 61.67%. Also for all the relative humidity and
at all days of storage levels, moisture content and
microbial count decreased with increase in polythene
thickness wh ile qua lity index increased w ith increa se in
polythene thickness. C onsidering 47.2% relative hum idity
and storage day 14, moisture content decreased from 4.54
for the control to 2.1 1% db at polythene thickness of
0.95mm, microbial count decreased from 1100 to 120
CFU/g while quality index increased from 63 to 80.25%.
The analysis off variance (Table 2) shows highly
significant (P#0.01) relative hum idity (RH) effect on
moisture content and q uality index while microbial count
is non-significant. In terms of moisture content, a 2-tailed
F-LSD test at 5% level of significance between 7-28 days
of storage and four levels of polythene thicknesses
representing 16 mean comparisons shows that between
47.2 and 7 0.4 %RH, 31.25% of the mean comparisons
were non-significant. Similarly, 43.75% non-significance
was observed in the mean comparisons between 70.4 and
Effect of Duration of Storage: The results show that the
moisture content of all the samples increa sed w ith
increase in duration of sto rage at constant polythene
thickness level (Table 1). For storage days range of 0 to
28 at constant polythene thickness of 0.95mm, moisture
content at 47.2% RH increased from 1.17 to 8.65, 70.4%
RH from 1 .17 to 9.70 an d for 80 .5%RH from 1.17 to
10.75%db. Similarly, microbial count increased from 30
to 1060, 30 to 3130 and 30 to 14600 CFU/g for 47.2, 70.4
and 80.5%RH respectively whereas quality index
decreased from 1 00 to 6 9.34, 100 to 67.17 and 1 00 to
63.16% at same % RH values.
151
Res. J. Appl. Sci. Eng. Technol., 1(3): 149-153, 2009
Tab le 1:
Mean values for moisture content, microbial count and quality index as affected by relative humidity, polythene thickness and duration
of storage*
Re lativ e H um idity , %
Polythene Thickness, mm
Duration of S torage (Days)
------------------------------------------------------------------------------------0
7
14
21
28
Moisture Content (%db)
47 .2
Control
1.17
2.77
4.54
9.25
14.76
0.91
1.17
2.56
3.01
6.00
9.61
0.93
1.17
2.24
2.87
5.60
9.42
0.95
1.17
1.97
2.11
5.50
8.65
70 .4
Control
1.17
3.41
5.63
9.63
15.97
0.91
1.17
3.00
3.08
7.18
10.95
0.93
1.17
2.67
3.07
6.30
10.86
0.95
1.17
2.65
2.78
6.18
9.70
80 .5
Control
1.17
4.15
6.84
9.89
17.02
0.91
1.17
3.41
3.81
7.19
11.75
0.93
1.17
3.16
3.78
6.80
11.00
0.95
1.17
3.13
3.39
6.74
10.75
Microbial count (CFU/g)
47 .2
Control
30
700
1100
2800
3660
0.91
30
400
520
1800
2100
0.93
30
300
487
1100
1580
0.95
30
120
120
1000
1060
70 .4
Control
30
850
2700
8500
21950
0.91
30
500
800
1900
15790
0.93
30
425
500
1530
12350
0.95
30
180
200
1200
3130
80 .5
Control
30
950
12400
22600
31860
0.91
30
580
9700
15400
16400
0.93
30
500
2500
14800
15100
0.95
30
310
500
10700
14600
Q ua lity In de x (% )
47 .2
Co ntro
l100
67.67
63.00
56.00
48.00
0.91
100
75.50
71.00
65.34
61.67
0.93
100
79.00
74.25
68.00
65.33
0.95
100
82.00
80.25
70.33
69.34
70 .4
Control
100
63.00
60.00
52.00
40.00
0.91
100
73.00
67.34
65.00
56.67
0.93
100
76.50
70.50
66.67
61.66
0.95
100
80.00
76.25
68.00
67.17
80 .5
Control
100
57.00
50.00
35.00
32.00
0.91
100
68.00
63.45
59.50
52.17
0.93
100
70.00
66.25
62.50
60.00
0.95
100
74.00
71.00
64.67
63.16
*Values are means of three replications
Fishers Least Significant Difference (F-LS D) Moisture Content (% db) F-LSD (P=0.05) of the d ifference between tw o relative humidity means =
0.547; F-LSD (P=0.05) of the difference between two polythene thickness means = 0.843; F-LSD (P=0.05) of the difference between two duration
of s to r ag e m eans = 1.346 To tal fung al cou nt (C FU /g) F-LSD (P=0.05) of the difference between two relative humidity means = 6355.3; F - L SD
(P=0.05) of the difference between two polythene thickness means = 2192.9; F-LSD (P=0.05) of the difference between two duration of storage means
= 6853.0 Qu ality Ind ex (% ) F-L SD (P= 0.05 ) of th e diff eren ce b etw een two relativ e humidity means = 3.179; F-LSD (P=0.05) of the difference
between two polythene thickness means = 3.451; F-LSD (P=0.05) of the difference between two duration of storage means = 5.848
Table 2: Summary of AN OV A for moisture content, microbial count and quality index
Source of Variation
Degree of Freedom
Moisture Content (%db)
Microbial Count (CFU/g)
Duration of Storage
4
371.36**
3.80*
Relative Humidity
2
10.74**
3.81 N S
Error (a)
8
Polythene T hickness
3
17.42**
8.21*
Interaction
6
0.03 N S
1.46 N S
Error (b)
36
**Highly significant difference (1%), * Significant difference (5%), NS Non significant
The analysis of varian ce (Table 2) show s highly
significant (P#0.01) duration of storage effect on moisture
content and quality index while microbial count is
considered significant (P#0.05). A 2-tailed F-LSD test at
5% level of significance from 0-28 days of storage shows
that for the 6 mean moisture content comparisons, all
comparisons were different on day 7 while 33.33, 50 and
33.33% non-significant differences were observed on
days 14, 21 and 2 8 respectively at 47.2%RH. How ever, at
70.4%RH, 100, 50, 16.67, 16.67 and for 80.5%RH , 66.67,
50, 50, 33.33% mean comp arisons w ere found to be non-
Q ua lity In de x (% ) 5%
183.41**
2.78
14.79**
5.14
1%
4.22
10.19
34.06**
0.62 N S
9.78
3.36
4.76
2.36
significant on days 7, 14, 21 and 28 respectively. In the
case of the microbial count, all the comparisons at
47.2%RH were statistically different excep t on day 28
between control and 0.95mm where non-significance was
observed. In the case of 70.4%RH , 100, 66.67, 50, 100
and for 80.5%RH , 100, 16.67, 16.67, 50% nonsignificance was recorded for control, 0.91, 0.93 and
0.95mm respectively. For quality index, 16.67% nonsignificance was observed on days 7, 14 and 28 at
47.2%RH with 33.33% on day 21. At 70.4%RH, the
index was 16.67% and 50% non-significant on days 14
152
Res. J. Appl. Sci. Eng. Technol., 1(3): 149-153, 2009
and 21 respectively while on days 7 and 28, all the
differences were statistically different. In the case of
80.5%RH, quality index indicated 16.67% nonsignificance difference on days 7, 14 and 28 while on day
21, 66.67% non-significant difference was observed.
C
Practical Industry Applications: From the resu lts
obtained from the moisture content on each test day and
at all %RH values, taking 5.8%db as the moisture content
threshold value which is considered as the maximum
permissible percentage amount of moisture for safe
storage of roasted cashew nuts ( Henderson, 1985; Pixton,
1986), the shelf life of the nuts was deduced to be less
than 21 days irrespective of the storage %RH and
thickness of the polythene packaging material excluding
that packaged in mosquito net (contro l) which had a shelf
life of less than 21 day s at storage % RH of 47.2 and less
than14 days at storage %RH s of 70.4 and 80.5. W ith
reference to quality, irrespective of the polythene
thickness excluding the control, the stored roasted cashew
nuts still remained edible after 28 days as the percentage
quality index did not drop below 45% which was set as
the lowest acceptable percentage quality index. In
accordance to ICMSF(1986), the maximum set fungal
tolerance acceptable for packaged nuts fit for human
consumption is 104 /g. Based o n the results, the shelf-life
of the nuts stored in polythene thicknesses of 0.91, 0.93
and 0.95mm was 14 days as the results beyond day 14
exceeded the tolerable fungal count. Conversely the nuts
stored under the control had a shelf-life of 7 days. The
nuts stored in 0.95mm , which is the thickest polythene,
absorbed the least amount of moisture; had the smallest
total fugal count, and the highest percentage quality index
at all %RH and day of storage levels in comparison with
the values obtained from the other less thicker polythene.
This is followed by nuts stored in 0.93mm, 0.91mm and
control in that order. The results further show that the rate
of deterioration of the nuts increased with higher storage
RH. Considering the three storage RH used in the study,
the most favourable storage RH irrespective of the
thickness of the packa ging m aterial is 47 .2% . Adebajo
(1992) found out that the highest tolerable RH for
polythene packaged foods (including nuts) is 70%, if the
moisture content is to be maintained below 5.8% db for a
reasonable length of time.
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Tropical Stored Products Inf., 43: 16-29.
W east, R.C. and M. J. Astle, 1979. CRC Handbook of
Chemistry, 62 n d Edition. CRC Press Inc. Bana,
Raton Florida.
CONCLUSIONS
Based on the results obtained in this study the
following conclusions are drawn:
C
C
quality index decreased with increase in duration of
storage. As the polythene thickness increased at
constant storage duration, the moisture content
decreased. The moisture content of all the samples
increased with increase in duration of storage at
constant po lythene thickness level.
For packaged roasted cashew nuts industry for
poverty alleviation, the most favourable storage
relative humidity is 47.2% with polythene thickness
of 0.95mm. Storage period should not exceed 14 days
for best quality and value for money.
There is highly significant effect of relative humidity,
polythene thickness and duration of storage (P#0.01)
on moisture content and quality index while for the
microbial count, polythene thickness and duration of
storage has significant effect (P#0.05) with relative
humidity showing non-significance.
For all levels of relative humidity and polythene
thickness, moisture content and microbial count
increased with increase in duration of storage while
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